Base catalyzed polymerizations



Patented Aug. 26, 1952 "UNITED ST Orville Horwitz Bullitt, Jr., Swarthmore, Pa., a'ssignor to E. I. du Pont de Nemours & Company,

Wilmington, DeL, a corporation of Delaware No Drawing. Application July 3,1948,

Serial No. 37,060

This invention relates to a new process for the polymerization of monoethylenic compounds.

This invention. has as an object an improvement in the polymerization of monoethylenic compounds. Other objects will appear hereinafter.

. These objects lowing invention wherein a polymerizable monoethylenic compound, i. e., a polymerizable compound, havingflbutone unsaturated carbon to carbonlinkage of aliphatic character and that ethylenic, is, polymerized by bringing the same in contact, .ata temperature below 10, C. and above -l20, C. in an anhydrous, inert medium, with a catalytic amount, 0.01 to based on the weight of polymerizablermonomer, of a salt, with an alkali forming metal, an. acid having a pK- of-at least 15 [Ha-mmett, Physical Organit Chemistry, McGraw-Hill (1940), pages, 48-50, 251- 290]. The term pKs has been discussed and defined by Conant et al., J. Am. Chem. Soc. 54, 1212 (1932),; McEwen, ,ibid, 58; 1124 1(1936);

Branch and, ,Calvin- -The, Theory of Organic Chemistry (Prentice-Hall, 1936) pages: 183-270.

In a-preferred ,methodof practicingthis ill-r] ventionthe polymerizable monoethylenic oompounchsuch as methyl methacrylate or,methac-.

rylonitrile is rapidly agitated in, liquid jam moniaata temperature, of -90:, to 33 C. in.

the presence of a small amount, such as 0.1 to 2%, of a strong base such as potassium amide or sodium amides Aftera short time, such as fIQm three minutes to three hours,;the strong base, is,neutralized, e. g with an acid such as ammonium chloride, and the solid polymer iso-. lated by removal: of the liquid ammonia and any monomer that may remain.

flfhe iollowing examples in which parts are by weightare illustrative of the invention.

of'fanhydrous liquid ammonia was stirred under nitrogen fat, .-'l' 7 Cl for "five minutes, during which'time the sodium was converted to sodamide, due to the catalytic effectof sodium oxides present] To thissolution there wasadded with stirring over a period of about three minutes a total of 20 parts of methacrylonitrile. Polymerii'zation,Qccurred'immediately on addition and. the polymeric product precipitated. After fifteen. minutes; excess ammonium chloride was added and, after, stirring five minutes the polymer was removed by filtration on a Buchner funnel. I The precipitate ,was then stirred .in Water, washed with ethanol, ethanol-hydrochloric acid mixture, 'ethan'oLand ether, "and dried iii a vacuum.

are accomplished by the role I 2 Claims. lcl. zen-789.5)

. H '40 Alsolutionof 0.1 part of sodiurnin 410 parts There was obtained methacrylonitrile which had a molecular weight of 83,000, as indicated by the viscosity of an 0.1% solution in dimethylformamide. 1

Example II To a solution of 0.1 part of sodium in 410 parts of anhydrous liquid ammonia inwwhich' the sodium had been converted to sodium:

amide by addition of ferric nitrate, there was added, in two minutes with stirring at -.77 C.,;

a total of 23.5 partsv of methyl methacrylate.

Solid polymeric product separated and afterllten. minutes stirringthe solid was removed by filtraa tion on a Buchner funnel. The aproductilwas V washed twice with 50% aqueous; ethanolnthen twice with 50% aqueous ethanol containing;

hydrogen chloride, thentwice With 50% aqueous; ethanol. The White, powdery polymer wasdried; in a, vacuum and consisted of 21 parts of acetone-5,

soluble product which had a molecular weight 01;;

43,000, as determined by the method of lizg igen v dale, Bywater, and Evans [J Polymer (1946) l.

Example III About ten parts of methacrylonitrile was dissolved in about 30 parts of trimethylami'ne and the solution cooled to C. Addition of 'aboutl two partsloffa 5% solution of phenyllithiuminether resulted in rapid conversion toa yellow solid product inhigh yield. Similar results were.

obtained when acrylonitrile was substituted for: methacrylonitrile in the above procedure.

Example IV About 410 parts of liquid ammonia (distilled Example V N H A To a vigorously stirred solutionof flO par-ts'bI: dry acrylonitrile maintained-ataboutfi C. was added dropwise a saturated solution ofsodiuin r'nethoxide in methanol;- After'the addition-or a 18.6 parts of polymeric 3 few drops of the solution the temperature rose rapidly to 30 C. The reaction mixture was again cooled to 5 C. and a few more drops of the initiator solution added when a similar temperature rise was noted. About 0.5 part of sodium methoxide-inabout 2 parts of methanol was used in all. A large excess of ethanol and water was then added and the product was separated by filtration, washed in succession with alcohol, 6-N- hydrochloric acid solution, water, ethanol and diethyl ether. In this way six parts of apale yellow powder was obtained which was soluble in di methyl formamide to give a solutionirom which a clear film was obtained on casting by conventional methods.

reaction temperature had again fallen to 32 C.

and 0.1 partof initiator solution was added raising thetemperature to -17 C. The total time of the reaction was twenty-five minutes, at the end of which the'mixture was treated with Water and ethanolc'jThe product was separated by filtration and washed with alcoholic hydrogen chloride 'ethanol and diethyl ether. Ther was obtained 19.5 parts of a white powder from which a clear yellow film was obtained by heating at 190 C. under pressure. The molecular weight ofthe polymer was 17,000. A solution of the polymer in dimethyl formamide yields a clear pale yellow film.

Emamp'le VII To a. rapidly-stirred dispersion of 80 parts of acrylonitrile in 300 parts of, butane at 85 C.

therewas. added 15 parts of an ether-solution containing 1.5 parts of lithium diphenylamide.

The addition of. the initiator solution required seuentyminutes during which the temperature of the reaction mixture was maintained between 85 and: 70 C. At the end of the reaction period the polymeric product was recovered in the manner described in Example VI to give 42 parts of a pale green powder-havin a molecular weight 0178.000.

' Example VIII I Adispersion of 40 parts of acrylonitrile in 100 parts of 'butanewas stirred rapidly while 7 parts of; anether solution containingOJI part of phenyllithium was added during twenty minutes. The temperature was maintained between 68 and 72 C. When the product was isolated as described in Example. VI a total of 3.5 parts of a paleyellow powder having a molecular weight oi- 23,000 was; obtained.

Example IX To about 1.4 parts -of-potassium amide in 572 parts of, liquid ammonia-in aS-necked round bottom flask protected from moisture by a drying tube was added slowly with stirring, '130 parts of distilled acrylonitrile. ,A vigorous reaction oc- The polymer was insoluble in cyclohexanone and concentrated hydrochloric parts) was stirred in a nitro Escample X Styrene was polymerized in a manner similar to that described above using 0.0125 mole of potas- 'sium amide and 1 mole of styrene. A 91% yield of polystyrene (molecular weight 5100) was obtained.

In the process of this invention there isrem ployed as the initiator for the polymerization of polymerizable monoethyl'enic compounds the salt, with an alkali forming metal, of an acidihavi-ng a pKa of at least (Hammett, pages 4950). and

generally less than 75, including not only the compounds listed in Hammett, Branch .et' al.,

Conant et al., and McEwen supra, but all :such compounds so defined. The preferredinitiators are the group IA metal salts of such acids, which include. particularly the alkali metal alkoxides,'- aryls, and amides, e. g., sodium methoxide, potassium methoxide, sodium ethoxide, sodium.ter-' tiary-butoxide, phenyllithium, lithium ethylphenylamide, potassium amide, lithium diphenylamide, and indenyllithium. Other initiators include the salts, with alkali forming metals, L e, group IA and, group IIA metals, of alkanes, ara'lkanes, amines, nitriles, etc;, e. 'g., ethylsodium,

dianilinecalcium.

The strong bases used as initiators in this in vention may be prepared in a variety of ways which are well described in the literature. One

methodof preparation of a base involves the synthesis of 'phenyllithium from bromobenzene" and lithium metal, as described by Gilman, -J.'

Am. Chem. Soc. 54, 1957 (1932). The phenyllithium made in this way is obtained in ether sold-- tion, which is suitable for use directly in the practice of this invention. By the addition of suitable amounts of acids stronger than benzene to this ether solution, a large number of initiator" solutions may readily be prepared in a conven ient form.

The temperature of the polymerization should bebetween 10 and 120 C., with a preferred range of from to -90 C. At these lower temperatures polymers of higher degree of polymerization are obtained. The polymerization may be run in bulk or in inert solvents or diluents, such as ammonia, trimethylamine, and

ether. Since initiators which are particularly efiective in the practice of this 'inventionfare readily decomposed by water and other active hydrogen-containing materials, the presence of these substances in other than small amounts is to be avoided, particularly if high-molecular weight products are desired; 1. e., the polymeri zation is conducted essentially in the absence of more than 10%,. based on the polymerizablei monomer, of active hydrogen-containingmaterials which have a pKsof 30 to 15, and in the sub-' stantial absence of any material having a pKa less than that of the conjugate acid of the basic catalyst. Ifmethanol or other alcohol is used as a solvent for the initiator, its concentration should be kept at a minimum, preferably below based on the polymerizable monomer.

The alkali forming metal salt is present only in catalytic amounts, 1. e., from 0.01 to 5%, and preferably from 0.1 to 2% based on the Weight of polymerizable monomer. Smaller amounts may require longer periods of time for the polymerization, while larger amounts give lowmolecular-weight products or insoluble or crosslinked polymers.

The time required for the polymerization is usually short, e. g., from one to thirty minutes, although longer times may be employed but are usually unnecessary.

The monomeric compounds subject to polymerization and copolymerization by the process of this invention consist solely of monoethylenic compounds which are liquid or soluble under the reaction conditions and which are polymerizable to macromolecular polymers by conventional techniques, such as by peroxygen catalysts. Particularly preferred are the polymerizable monoethylenic esters and nitriles, particularly those having a terminal methylene group, e. g., methyl methacrylate, ethyl acrylate, butyl methacrylate, methacrylonitrile, and vinyl acetate.

The ease of polymerization is generally de pendent on the solvent for the polymerization system and the specific catalyst used. Optimum rates of polymerization of the polymerizable monoethylenic esters and nitriles are obtained in anhydrous liquid ammonia or a liquid amine, such as trimethylamine, system with sodium or potassium amide catalysts.

The polymeric products obtained by the process of this invention are useful in the preparation of fibers, films, and moldings. The prodnets are high-molecular-weight solids which generally have a degree of polymerization of at least 50 and preferably 100 or more, as defined by Staudinger and cited by Marval and I-lorning in 6 Gilmans Organic Chemistry, 2nd Ed. (1943), vol. I, page 741.

The foregoing detailed description has been given for clearness of understanding only and no unnecessary limitations are to be understood therefrom. The invention is not limited to the exact details shown and described for obvious modifications will occur to those skilled in the art.

What is claimed is:

1. In the polymerization of a methacrylic ester, the improvement wherein the polymerization iseflected by bringing said polymerizable compound in contact at a temperature within the range from C. to C. with the salt, With an alkali forming metal, of an acid of pi of 15 to 75.

2. In the polymerization. of methyl methacrylate, the improvement wherein the polymerization is effected by bringing said methyl methacrylate in contact at a temperature Within the range from -30 C. to -90 C. with the salt, with an alkali forming metal, of an acid of pKa of 15 to 75.

ORVILLE' HORWITZ BULLITT, JR.

REFERENCES CITED The following references are of record in the his of this patent:

UNITED STATES PATENTS Number Name Date 2,377,779 Hanford -1 June 5, 1945 2,458,355 Dickey Jan. 4, 1949 2,475,424 Dickey et al. July 5, 1949 2,478,416 Miller Aug. 9, 1949 OTHER REFERENCES GlasstoneTextbook of Physical Chemistry- 2nd Ed, pages 974-975.

Wooster, 56 J. Am. Chem. Soc. 1134-1136, May 1934. 

2. IN THE POLYMERIZATION OF METHYL METHACRYLATE, THE IMPROVEMENT WHEREIN THE POLYMERIZATION IS EFFECTED BY BRINGING SAID METHYL METHACRYLATE IN CONTACT AT A TEMPERATURE WITHIN THE RANGE FROM -30* C. TO -90* C. WITH THE SALT, WITH AN ALKALI FORMING METAL, OF AN ACID OF PKA OF 15 TO
 75. 